The much-discussed design technique that renders sites for all devices is proving its worth to some retailers. But is it the answer for all?

1-800-Contacts Inc. is one e-retailer that put responsive to the test. In early 2013, the web-only merchant pitted its existing smartphone-optimized site against a new responsive design site, splitting mobile traffic between the two. A few months later, the verdict was in: the smartphone site was retired, the responsive site won.

"Conversion rates improved, and we only have to manage one code base and one set of analytics instead of having tags from multiple platforms," says Phil Barrett, the retailer's senior vice president of e-commerce and mobile. "Mobile is changing so fast that a responsive experience allows us to scale, adopt and convert on all screen sizes and form factors."

The old ways of designing for web commerce won't cut it any longer, Barrett says. "In the future, all online shopping will be mobile," he says. "We're trying to get ahead of it and put our best mobile offerings in place."